TIL subshell

I wanted to execute a python scraper without having to navigate to the folder, activate the virtual environment (venv), and run the script.

So, I created an alias to do this.

alias canirecycle='cd /Users/minho/code/python/return-and-earn && activate && python main.py'

~
❯ canirecycle
Checking for woolworths-marsfield...
Glass:          Full | Not Busy
Plastic & cans: Full | Not Busy
 
~/code/python/return-and-earn
(return-and-earn) ❯

It worked, but after running the aliased command, I was moved to the directory where the file exists, and the venv remained activated. I asked ChatGTP if I could do it without changing my current working directory. The solution was very simple: use parentheses ().

alias canirecycle='(cd /Users/minho/code/python/return-and-earn && activate && python main.py)'

~
❯ canirecycle
Checking for woolworths-marsfield...
Glass:          Full | Not Busy
Plastic & cans: Full | Not Busy
 
~
❯

The parentheses () create a subshell that temporarily changes the directory, activates the virtual environment, and runs the script. After the subshell completes, it exits, and you remain in your original directory.

See also

https://www.geeksforgeeks.org/shell-scripting-subshell/

Placing a list of commands between parentheses forces the shell to create a subshell, and each of the commands in list is executed in that subshell environment.

https://www.geeksforgeeks.org/shell-scripting-subshell/

One useful feature of subshells is that they allow you to isolate the effects of certain commands or operations. For example, you can use a subshell to set temporary variables or change directories without affecting the parent shell’s environment.